A storage system typically comprises one or more storage devices into which information may be entered, and from which information may be obtained, as desired. The storage system includes a storage operating system that functionally organizes the system by, inter alia, invoking storage operations in support of a storage service implemented by the system. The storage system may be implemented in accordance with a variety of storage architectures including, but not limited to, a network-attached storage environment, a storage area network and a disk assembly directly attached to a client or host computer. The storage devices are typically disk drives organized as a disk array, wherein the term “disk” commonly describes a self-contained rotating magnetic media storage device. The term disk in this context is synonymous with hard disk drive (HDD) or direct access storage device (DASD).
The storage operating system of the storage system may implement a high-level module, such as a file system, to logically organize the information stored on volumes as a hierarchical structure of storage objects, such as files and logical units (LUs). A known type of file system is a write-anywhere file system that does not overwrite data on disks. An example of a write-anywhere file system that is configured to operate on a storage system is the Write Anywhere File Layout (WAFL®) file system available from NetApp, Inc. Sunnyvale, Calif.
The storage system may be further configured to allow many servers to access storage objects stored on the storage system. In this model, the server may execute an application, such as a database application, that “connects” to the storage system over a computer network, such as a point-to-point link, shared local area network (LAN), wide area network (WAN), or virtual private network (VPN) implemented over a public network such as the Internet. Each server may request the data services of the storage system by issuing access requests (read/write requests) as file-based and block-based protocol messages (in the form of packets) to the system over the network.
A plurality of storage systems may be interconnected to provide a storage system architecture configured to service many servers. In some embodiments, the storage system architecture provides one or more aggregates, each aggregate comprising a set of one or more storage devices (e.g., disks). Each aggregate may store one or more storage objects, such as one or more volumes. The aggregates may be distributed across a plurality of storage systems interconnected as a cluster. The storage objects (e.g., volumes) may be configured to store content of storage objects, such as files and logical units, served by the cluster in response to multi-protocol data access requests issued by servers.
Each storage system (node) of the cluster may include (i) a storage server (referred to as a “D-blade”) adapted to service a particular aggregate or volume and (ii) a multi-protocol engine (referred to as an “N-blade”) adapted to redirect the data access requests to any storage server of the cluster. In the illustrative embodiment, the storage server of each storage system is embodied as a disk element (D-blade) and the multi-protocol engine is embodied as a network element (N-blade). The N-blade receives a multi-protocol data access request from a client, converts that access request into a cluster fabric (CF) message and redirects the message to an appropriate D-blade of the cluster.
The storage systems of the cluster may be configured to communicate with one another to act collectively to increase performance or to offset any single storage system failure within the cluster. The cluster provides data service to servers by providing access to a shared storage (comprising a set of storage devices). Typically, servers will connect with a storage system of the cluster for data-access sessions with the storage system. During a data-access session with a storage system, a server may submit access requests (read/write requests) that are received and performed by the storage system.
Each server may be within a specific storage site and each storage site may comprise multiple servers. Moreover, each server may execute numerous applications requiring the data services of the cluster. The data services of each server may be stored in data aggregates, such as flexible volumes. The data aggregates or flexible volumes may comprise a flexible volume hierarchy that may define a relationship between flexible volumes. For example, the flexible volume hierarchy may contain flexible volumes and clones of flexible volumes that relate to a base flexible volume.
The frequency with which storage objects within the system are accessed varies according to the usage patterns of the system, applications, and client devices that access the data stored on the storage objects. Permanent changes in the average level of utilization of a particular storage object may result from a variety of factors, including configuration changes within the system, configuration changes within the applications, or deprecation of application features. It is desirable to identify underutilized capacity within a storage system so as to efficiently re-allocate storage objects that are unused or accessed infrequently.
Though storage capacity that is dormant may sometimes be detected by, for example, tracking configuration changes that result in the deletion of a path, masking, or mapping to a storage object, capacity that becomes underutilized due to other, more subtle factors can be more difficult to identify. In one common scenario, a particular storage volume may only contain data pertaining to one application. If use of the application is discontinued or drastically reduced, the storage volume may become underutilized even though no configuration changes to the system have occurred. Thus, there is a need for a system and method that allows underutilized storage capacity within a storage system to be detected and identified.